Effects of UV-B and water deficit on the physiology and chemical composition of Vitis vinifera L. cv. Pinot noir : A thesis submitted in partial fulfilment of the requirements for the Degree of Doctor of Philosophy at Lincoln University

Abstract

New Zealand Pinot noir has seen impressive growth in export sales in recent years. It is now second only to Sauvignon Blanc in production volume. There are four main Pinot noir regions in New Zealand: Central Otago, Waipara, Marlborough and Wairarapa. In these regions, the soil, climate and other conditions are suitable for Pinot noir growth. However, some environmental issues challenge Pinot noir growth in New Zealand, such as water deficit and UV-B. The mean annual rainfall in regions where Pinot noir is grown, is low, and long dry spells can occur, especially in summer. UV-B radiation in New Zealand is 30-40% higher than at similar latitudes in the Northern Hemisphere. In this research, the aim was to determine effects of the separate and combined UV-B and water deficit on vine physiology and chemical composition of Pinot noir fruit. In the 2015-2016 and 2016-2017 vintages, two rows of Pinot noir grapevines in the West Vineyard at Lincoln University were chosen for the study. Treatments were a combination of leaf removal with plastic screens or shade cloth around the fruiting zone, and/or restricted irrigation. Grapevines and the fruit both responded to UV-B and water deficit. In comparison to exposure to natural UV-B in the vineyard, the potted vines were moved into a glasshouse for preparation for the experiments in September, prior to budbreak. From October (fruit-set) to December (veraison), the grapevines were uniformly irrigated on a regular basis to soil capacity and were exposed to normal daylength hours in the glasshouse. From veraison, vines in treatments were exposed to supplemental UV-B interaction with restricted irrigation in a glasshouse. The physiology of Vitis vinifera L. var. Pinot noir vines were altered by water deficit and UV-B. The combination of UV-B and water deficit changed the vine water status and leaf greenness in the glasshouse, but there was only a slight effect on berry parameters. However, UV-B exposure/exclusion interaction with water deficit did not affect vine water status and leaf greenness, even with no significant changes in fruit production capacity and °Brix in the vineyard. Amino acids did not show consistent results in the two-year trial. In the glasshouse, amino acids were decreased by UV-B and water deficit in 2015-2016. However, there was no change in amino acids in response to UV-B in 2016-2017. The concentration of amino acids under water deficit was enhanced by its combination with UV-B. In the vineyard, there were no changes in fruit amino acids with UV-B exposure or exclusion over the two years, but the interaction of UV-B with water deficit significantly changed His, Val, Thr and Lys in 2016-2017. Under UV-B and water deficit, vines were found to respond in both the glasshouse and vineyard trials. When berries were directly exposed to UV-B or water deficit, phenolic compounds accumulated to a greater degree in the berry skins. The combined stresses caused larger increases in phenolic composition than the individual stresses alone, such as skin anthocyanin contents in +UV-W (0.578 mg/berry) vs. -UV+W (0.398 mg/berry). A similar pattern was shown in the volatile compounds. For example, the concentration of hexanol was 1028.6 µg/L in +UV-W compared with 683.3 µg/L in -UV+W. Overall, this study clearly demonstrates that UV-B exposure can interact with water deficit to increase the effects on physiological parameters of the vine and fruit composition to UV-B or water deficit alone. Water deficit can, potentially, increase additional responses to UV-B in both glasshouse and vineyard situations.